make platformio.ini even more modular

arch/nrf52/nrf52840.ini

@@ -0,0 +1,14 @@
+[nrf52840_base]
+extends = nrf52_base
+build_flags = ${nrf52_base.build_flags} 
+lib_deps =
+  ${arduino_base.lib_deps}
+  ${environmental_base.lib_deps}
+  https://github.com/Kongduino/Adafruit_nRFCrypto.git
+
+; Note: By default no lora device is created for this build - it uses a simulated interface
+[env:nrf52840dk]
+extends = nrf52840_base
+board = nrf52840_dk
+
+